Observational evidence tells you that as a nova explosion begins, _____.

Observational evidence tells you that as a nova explosion begins, _____.
 
  A) a cloud of debris ejects into space
  B) matter settles inward onto the surface of a white dwarf and forms a layer of unused nuclear fuel
  C) dense gas comes toward you at a few thousand kilometers per second
  D) the spectral lines change to emission lines

Question 2

Stars less massive than about 0.4 solar mass are referred to as _____.
 
  A) brown dwarfs
  B) red dwarfs
  C) yellow dwarfs
  D) white dwarfs

Question 3

In the context of neutron stars, which of the following statements is true of pulsars?
 
  A) Neutron stars older than 10 million years rotate too slowly to generate detectable radio beams.
  B) When a pulsar first forms, it spins only around 10 times a second.
  C) As a pulsar blasts beams of radiation outward, its rotation speeds up.
  D) Supernova remnants last more than 150,000 years before they mix into the interstellar medium and disappear.

Question 4

Observations and stellar evolution models indicate that the central star of a planetary nebula finally must contract and become a _____.
 
  A) yellow giant
  B) white dwarf
  C) red giant
  D) black dwarf